/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

namespace Lucene.Net.Util
{
    
    /// <summary>Java's builtin ThreadLocal has a serious flaw:
    /// it can take an arbitrarily long amount of time to
    /// dereference the things you had stored in it, even once the
    /// ThreadLocal instance itself is no longer referenced.
    /// This is because there is single, master map stored for
    /// each thread, which all ThreadLocals share, and that
    /// master map only periodically purges "stale" entries.
    /// 
    /// While not technically a memory leak, because eventually
    /// the memory will be reclaimed, it can take a long time
    /// and you can easily hit OutOfMemoryError because from the
    /// GC's standpoint the stale entries are not reclaimaible.
    /// 
    /// This class works around that, by only enrolling
    /// WeakReference values into the ThreadLocal, and
    /// separately holding a hard reference to each stored
    /// value.  When you call {@link #close}, these hard
    /// references are cleared and then GC is freely able to
    /// reclaim space by objects stored in it. 
    /// </summary>
    
    public class CloseableThreadLocal
    {
        
        [ThreadStatic]
        static SupportClass.WeakHashTable slots;
        
        public /*protected internal*/ virtual System.Object InitialValue()
        {
            return null;
        }

        public virtual System.Object Get()
        {
            object value;

            if (slots == null)
            {
                value = InitialValue();
                if (value != null)
                    Set(value);

                return value;
            }

            if (slots.ContainsKey(this))
            {
                return slots[this];
            }
            else
            {
                value = InitialValue();
                slots[this] = value;
                return value;
            }
        }
        
        public virtual void  Set(System.Object object_Renamed)
        {
            //+-- For Debuging
            if (SupportClass.CloseableThreadLocalProfiler.EnableCloseableThreadLocalProfiler == true)
            {
                lock (SupportClass.CloseableThreadLocalProfiler.Instances)
                {
                    SupportClass.CloseableThreadLocalProfiler.Instances.Add(new WeakReference(object_Renamed));
                }
            }
            //+--

            if (slots == null)
                slots = new SupportClass.WeakHashTable();

            slots[this] = object_Renamed;    
        }
        
        public virtual void  Close()
        {
            if(slots != null)
                slots.Remove(this);
        }
    }
}